This invention relates generally to separation of gases, and more particularly to improvements in method and apparatus to centrifugally separate gaseous streams.
Nearly every source of natural gas has carbon dioxide, CO2, as an impurity. The major hydrocarbon constituent of natural gas is methane, CH4. For some sources the percentage of CO2 may be as high as 70% while the methane component is only 30%. In order to process natural gas, the CO2 content must be reduced. Current methods of reduction include absorption in a chemical solution or use of membranes. Both of these methods are costly and require a large amount of equipment and space. For offshore production and processing of natural gas, the cost and space requirements of these conventional methods of CO2 reduction can result in an uneconomic project, reducing the recovery of the natural gas.
The possibility of using centrifugal force to separate gases was first suggested by Redig in 1895. Once isotopes were found to exist in 1913, centrifuges surged as a method of separating different isotopes by separating gaseous components. Beginning in the 1930""s and through the Manhattan Project in the 1940""s gaseous centrifuge research was directed to the enrichment of Uranium 235 for use as nuclear fuel.
Although the United States abandoned the method of centrifugal separation, preferring gaseous diffusion instead, the Soviet Union and a coalition of European nations continued to research gaseous centrifuges and eventually established plants of industrial capacity using such technology to produce enriched uranium. Recently, work has been done to separate other isotopes for use in, for example, the medical field.
Yet the possibility of using gaseous centrifuges as disclosed herein for the separation of two completely different gases has never seriously been explored. If such a system of gaseous centrifuges were provided and operated to separate two (or more) chemically different (as in not just different isotopes of the same element), the apparatus, as provided herein, would be physically smaller and would require less resources than alternative methods which are in use today, thus providing an economically best choice.
It is a major object of the invention to provide method and means for separating mixtures of gases into their components, in an improved and highly efficient way, or manner.
A gaseous centrifuge is a relatively small, enclosed device that rotates at extremely high speeds (upwards of 30,000 RPM) which takes advantage of centrifugal force to separate a mixture of gases. Once a mixture of gases is fed into such a centrifuge, a radial concentration gradient is established in which the heavier gas is at higher concentration (than the input stream) at the periphery and the lighter gas is at a higher concentration (than the input stream) in the region closer to the axis of rotation.
The partial pressure of a gaseous component in a centrifuge, assuming solid body rotation is given from the Maxwell-Boltzmann Distribution Laws as:
pi (r)=p1 (0)exp[Mi (xcexa9r)2/2RT]
where:
p1=partial pressure of component 1 at
location ( )
Mi=molecular weight of component 1
xcexa9=angular velocity
r=radius
R=gas constant
T=temperature
Comparing the concentration of two gaseous components gives:
xcex1=exp[(M2xe2x88x92M1)(xcexa9r)2/2RT]
where:
xcex1=ratio of concentration of component 2 to component 1
M2 =molecular weight of component 2
M1=molecular weight of component 1
For separation of isotopes such as uranium 235 and uranium 238 the molecular weight difference is only 3 units resulting in a relatively small concentration factor and a huge number of concentration stages required to effect a substantial concentration. However, for mixtures of carbon dioxide and methane, the molecular weight difference is
M2xe2x88x92M1=44xe2x88x9216=28
This produces a large concentration ratio compared to typical isotope separations. Consider a speed of 3000 radians/second, a cylinder radius of 10 cm and a temperature of 300xc2x0 K. For uranium 235 and uranium 238 separation, the concentration ratio is:
xcex11=exp[(3)(300)2/(2) (8314)(300)]=1.056
For CO2 and CH4 the concentration ratio is:
xcex11=exp[(28)(300)2/(2) (8314)(300)]=1.657
Thus, an unexpected result as disclosed herein is found in applying a centrifuge to separate carbon dioxide from methane in that an extraordinary increase in concentration can be accomplished compared to isotopic separation.
Accordingly, another major object is to provide a gas centrifuge means operating to separate gases of differing chemical composition and molecular weight by a centrifugal force field. Typically, and in accordance with a further feature of the invention, carbon dioxide is separated from methane by an improved method employing a centrifugal force field.
Another object is to provide a multiplicity of centrifuge means as defined in claim 1, arranged such that the separated streams of gases are further concentrated by introducing them into successive of the gas centrifuge means.
An additional object is to provide a gas processing system utilizing centrifugal force for the separation of light gases from heavy gases, liquids from gases, light liquids from heavy liquids and solids from liquids and gases.
An additional object if to provide a gas centrifuge apparatus comprising, in combination:
a) a hollow shaft to pass and introduce a gas mixture into a rotating cylinder,
b) said cylinder having axial vanes to cause the gas mixture to rotate with the same angular speed as the cylinder,
c) a radial passage connected to the periphery of the cylinder to receive and pressurize a produced and concentrated heavier gas stream,
d) a nozzle connected to the passage to convert the pressure of the heavier gas stream to velocity adding a torque to the cylinder, and
e) an opening in the hollow shaft to receive and remove a produced and concentrated lighter gas stream from the cylinder.
A yet further object is to provide an improved centrifuge apparatus operating in the manner referred to, and incorporating:
a) a nozzle accelerating a gas mixture and introducing it into a rotating cylinder, adding torque to the cylinder,
b) the cylinder having vanes to receive torque from the gas and causing the gas to rotate with the same angular speed as the cylinder,
c) a radial passage connected to the periphery of the cylinder operating to pressurize a produced and concentrated heavier gas stream,
d) a nozzle connected to the passage and operating to convert the pressure of the heavier gas stream to velocity, adding torque to the cylinder,
e) an open scoop oriented perpendicular to the direction of rotation operating to remove a produced and concentrated lighter gas from the cylinder, and
f) a passage contoured and operating to recover the velocity head of the concentrated lighter gas as pressure.
A yet further object is to provide an improved centrifuge apparatus operating in the manner referred to, and incorporating;
a) a nozzle accelerating a gas mixture and introducing it into a rotating cylinder, adding torque to the cylinder,
b) the cylinder having vanes to receive torque from the gas and causing the gas to rotate with the same angular speed as the cylinder,
c) a radial passage connected to the periphery of the cylinder operating to pressurize a produced and concentrated heavier gas stream,
d) a nozzle connected to the passage and operating to convert the pressure of the heavier gas stream to velocity, adding torque to the cylinder,
e) a radial passage connected to the periphery of the cylinder, extending radially inward such that its inlet is at the region of concentration of the lighter gas and operating to pressure a produced and concentrated lighter gas stream,
f) a nozzle connected to the radial passage and operating to convert the pressure of the concentrated lighter gas to velocity, adding torque to the cylinder.
These and other objects and advantages of the invention, as well as the details of an illustrative embodiment, will be more fully understood from the following specification and drawings, in which: